The intension of this work was to investigate what conclusions we can make from a normal lung auscultation; where has the normal lung sound its origin and what anatomic and mechanic factors affect its transport from its site of origin to the chest wall? To do this I extracted the essence in a selection of articles found by a search in Medline on the keywords “lung sound”, “respiratory sounds” and “auscultation”. The text includes a mechanical understanding of sound production and transport, a historical review on auscultation and an up to date understanding of a normal lung auscultation.
Lung sounds originate in large- and medium-sized airways where turbulence replaces the laminar airflow. The lung sounds are transported to the chest surface through air spaces, parenchyma and the chest wall. The generation is affected by lung volume and by the velocity and direction of airflow. Regional distribution, ventilation and closing volumes influence lung sound intensity at different areas of the chest surface and at different times of the respiratory cycle. Individual anatomic variations within the chest cavity affect the transmission to the chest surface, and the density of pulmonary parenchyma impacts on the propagation and attenuation of sound.